Mystery of Bizarre Duck-Like Ocean Sound Solved

Below:

Next story in Science

A mysterious duck-like sound recorded in the ocean around
Antarctica has baffled scientists for decades, but the source of
the sound has finally been found, researchers say.

For more than 50 years, researchers have recorded the so-called
"bio-duck" sound in the Southern Ocean. Submarine crews first
heard the oceanic quack, which consists of a series of
repetitive, low-pitched pulsing sounds, in the 1960s.

"In the beginning, no one really knew what it was," said Denise
Risch, a marine biologist at NOAA Northeast Fisheries Science
Center in Woods Hole, Mass. Because the sound was so repetitive,
scientists first thought it might be human-made, possibly coming
from submarines. As time went on, people suggested a fish may be
making the sound, but it seemed too loud, Risch told Live
Science. [ Listen
to Mysterious Bio-Duck Sound ]

It turns out, Antarctic
minke whales actually produce the duck-like sound, Risch and
her colleagues have found. Years' worth of audio recordings will
now provide a wealth of information on the abundance,
distribution and behavior of these elusive cetaceans, the
researchers said in their study, detailed today (April 22) in the
journal Biology Letters.

Mystery quacks

The bio-duck sounds come in sets spaced about 3.1 seconds apart.
The noises also occur seasonally, and have been heard
simultaneously in the Eastern Weddell Sea off Antarctica and
Western Australia.

In February 2013, during the Southern Hemisphere's summer,
Risch's colleagues tagged two Antarctic minke whales
(Balaenoptera bonaerensis) off of Western Antarctica
with suction-cup tags. The researchers meant to study the whale's
feeding behavior and track their movements.

The tags also contained underwater microphones, and Risch
analyzed the acoustic recordings. She found they contained the
duck sounds, as well as downward-sweeping sounds previously
linked to the whales. The sounds "can now be attributed
unequivocally to the Antarctic minke whale," Risch and her team
wrote in the study. The researchers don't know for sure whether
the tagged whales or other nearby minke whales made the sounds.

What the sounds mean in whale-speak remains a mystery to
scientists. The whales may use the sounds for breeding or
navigation, Risch speculated. The researchers don't know, either,
whether only males make the sounds or females also partake. For
example, male humpback whales, unlike females, perform
complex songs during their mating season.

The fact that the sounds were heard off both Antarctica and
Western Australia suggests that some whales remain in Antarctica
year round, while others migrate to lower latitudes, as other
whales do, the researchers said.

Acoustic time capsule

Now that minke whales have been identified as the source of the
mysterious sounds in ocean recordings, researchers can use
those recordings to glean information about the distribution,
abundance and behavior of these vocal animals.

"The fantastic thing about acoustics is you can go back in time,"
Risch said.

The recordings will be especially useful in tracking these
animals in winter, when visual surveys are impossible due to
weather conditions. Researchers could put out buoys with
microphones during the summer, and later retrieve them to learn
about the whales' activity in colder months.

The ability to track minke whales acoustically also offers an
alternative research method to controversial
Japanese whaling practices, Risch said. "It shows killing is
not necessary."